1. Field of the Invention
The present invention relates to optical microscopes, and more particularly, to a microscope including an observation optical path for visual observation of an image and an image-acquisition optical path for recording an image.
This application is based on Japanese Patent Application No. 2005-126593, the content of which is incorporated herein by reference.
2. Description of Related Art
Conventionally, because the main application of microscopes has been observation with the eye, their optical specifications have been set within ranges suitable for visual observation (for example, see Principles of Biological Microscopes by Akihiro YOUKA, published by Baifukan, 20 Jun. 1973, Chapter 3, Objective Lenses).
According to Principles of Biological Microscopes by Akihiro YOUKA, published by Baifukan, 20 Jun. 1973, Chapter 3, Objective Lenses, the following expression gives the range of overall effective magnification for a microscope:400NA<M<1000NA
Here, NA is the numerical aperture, and M is the overall magnification.
The range given above indicates the range over which a suitable resolution can be obtained for visual observation; although there are also values outside of this range for various applications, products generally fall within this approximate range.
Recently, however, microscopes are not just being used for visual observation; their use as image-acquisition optical systems is becoming more and more common. In optical systems for image acquisition, the conventional concepts of effective magnification and empty magnification are not necessarily applicable.
In an image-acquisition optical system, for a constant overall effective magnification, the brightness of the image is proportional to the square of the numerical aperture. Therefore, a correspondingly bright image is obtained, and the exposure time is short. This is a particularly strong merit for taking images of specimens which move around, such as small living organisms, for which exposure must be completed within a short period of time.
On the other hand, if the range of overall effective magnifications is exceeded and a low magnification is set, not only is the resolution of the eye lower than the resolution of the optical system, thus not making full use of the resolving power of the microscope, but if the eye shifts when observing a comparatively deep specimen with the microscope, there is also a problem in that the image wobbles and becomes difficult to see.
Although there are differences in the way observers perceive things, this nevertheless causes unstable vision and may even result in nausea when observing for a long period of time. Therefore, the optical system for visually observing the image should preferably have specifications falling within the range of overall effective magnifications shown in non-patent document 1.